Rigid hubs for variable pitch rotors

ABSTRACT

THE HUB COMPRISES A ROTARY AXLE, A HUB BODY RIGIDLY SECURED TO THIS AXLE, AND ARMS FIXED TO THE HUB BODY, THE VARIABLE PITCH BLADES ARE FIXED TO THE FREE ENDS OF THE ARMS. EACH ARM COMPRISES AT LEAST THREE BUNDLES OF PILED STRIPS, THESE BUNDLES BEING DISTRIBUTED ABOUT THE PITCH VARIATION AXIS OF THE CORRESPONDING BLADE. THE BUNDLES OF ANY ONE ARM ARE CONNECTED TO EACH OTHER AND TO THE HUB BODY BY HOLDING MEANS-NAMELY RIGID COLLARS AND SHEETS-SUCH THAT THE ARM POSSESES A HIGH RESISTANCE TO FLEXION AND A RELATIVELY LOW RESISTANCE TO TORSION.

Sept 20, 1971 L. E. LERMuslAux RIGID HUBS FOR VARIABLE FITCH ROTORS 3 Sheets-Sheet 2 Filed Feb. 1C), 1969 E@ nl.;

@m Nmmn Nm. w

X u H l (v RU ON .IR N E W. L N l lh tu W Wa ATTORNEYS Sept 20 1971 L. E. LERMuslAUX 3,606,575

RIGID HUBS FOR VARIABLE FITCH ROTORS Filed FebulO. 1969 3 Sheets-Sheet l INVENTOR uic/EN E. LERMLLs/HLLX MMM M2M# ATTORNEYS Sept. 20, 1971 E. Lr-:RMuslAux 3,606,575

RIGID HUBS FOR VARIABLE PITCH ROTORS Filed Feb. .10, 1969 f s sheets-sheet s INVENTOR LLLclE/V E. LElmus/nux .iv/Y 'ATTORNEYS United States Patent O 3,606,575 RIGID HUBS FOR VARIABLE PITCH ROTORS Lucien Edmond Lermusiaux, Saint-Etienne, France, as-

signor to Societe de Construction et dExploitation de Materiels et Moteurs S.C.E.M.M., Paris, France Filed Feb. 10, 1969, Ser. No. 797,997 Claims priority, application grarlce, Feb. 12, 1968,

39,57 Int. Cl. B64c 27/38 U.S. Cl. 416-135 22 Claims ABSTRACT OF THE DISCLOSURE This invention relates to hubs for variable pitch rotors, lifting rotors, wind motors, fans and axial turbomachines, of the type which, devoid of articulations, are called rigid The invention is more particularly, but not exclusively, concerned with hubs of this type which are intended for rotor craft (helicopters, gyroplanes and the like Tire hubs to which this invention relates comprise a rotary axle, a hub body rigidly secured to this axle and arms fixed to the hub body. The rotor blades are fixed to the free ends of these arms. Each arm comprises at least three bundles of piled strips; these bundles are distributed about the pitch variation axis of the blade fixed to that arm.

An object of this invention is to provide hubs of the type in question which are adapted to absorb the high stresses which are applied to them by the blades that they carr Ayhub according to this invention is characterized by the fact that the bundles of strips of any one arm are connected to each other and to the hub body by holding means such that the arm possesses a high resistance to flexion and a relatively low resistance to torsion.

Various other features and advantages of the invention will become apparent from the following specific description, given with reference to the accompanying drawings, of a particular embodiment of the invention.

FIG. 1, of these drawings, shows, in a top view, an arm belonging to a rigid hub constructed according to the invention;

FIG. 2 shows, in a side view, with parts removed, this same arm;

FIG. 3 shows a schematic section along III-III of FIG. 2;

FIG. 4 shows, in section along IV-IV of FIG. 1, with parts removed, a detail of the arm; and

FIG. 5 shows, in perspective and schematically, the hub constructed according to this invention, with arms analogous to the arm of the preceding figures, in the absence of the braces of the arms, in order to clarify the drawing.

It is appropriate, first of all, to recall certain characteristics of the rotary aerofoils used for rotor craft and axial turbomachines, and a property of pieces constructed by a pile of sheets.

In addition to an overall movement of rotation with the axle of the hub, each of the blades of a rotor can 3,696,575 Patented Sept. 20, 1971 have to perform three sorts of movements. The first of these movements, called herealfter drag movement, moves the blade in the plane of rotation of the aerofoil ahead of or behind a substantially radial mean position. The second movement, called hereafter flapping movement, moves the blade in a plane containing this blade and perpendicular to the plane of rotation of the aerofoil. The third movement, called hereafter pitch variation, is a rotation of the blade about a longitudinal axis called hereafter pitch variation axis, the purpose of this rotation being to modify the angle of attack of the blade. This pitch Variation is composed of a general variation of pitch affecting all the blades of the rotating aerofoil in the same manner and possibly of a cyclic variation of pitch affecting each of the blades differently according to the position that the blade occupies with respect to the rotor craft which is equipped with these blades. These two variations are conrtolled by known mechanical. means.

It is known that metallic pieces working in alternate stress have a very variable limit of endurance due to the fact that this limit depends on local defects of manufacturing. Generally, bad workmanship or any other defect creates, during such stress, the be-ginning of a crack which propagates rapidly in the piece if this piece is composed of a single element.

If this piece is composed of a plurality of thin elements (thin sheets), glued together or not, and piled, the propagation of the cracks from one element to another is avoided. The rupture is thus avoided, or at least, it takes place after a time considerably longer than with a piece of similar shape but composed of a single element. This property is applied to the hub body of the rotor and to the arms. For the hub body of the rotor, piles of sheets, advantageously glued together, are used, whereas for the arms, the assembly is not effected by gluing.

With regard to the overall rotor, it comprises a rotary axle 1 (FIG. 5), a hub body 2, fixed to this axle 1 by appropriate means (not shown), arms 3, to which this invention is particularly directed, and blades 4 (three in number in the embodiment represented) fixed to the free ends of the arms 3. Y

With regard to the arms 3 (FIGS. l and 2), they are each constituted by at least three bundles 5, 6, 7 and 8, four in number in the example described, each composed of piled strips having the same shape in plan (their thicknesses can be different from one strip to another but constant for each strip) and disposed respectively along the edges of a pyramid or a prism, these bundles 5, 6, 7 and 8 being connected to each other and to the hub body 2 by holding means such that the arms 3 have a high resistance to flexion and a relatively low resistance to torsion.

These holding means comprise, for each arm 3, rigid collars constituted by groups of braces 11 disposed at a distance from each other in planes approximatively perpendicular to the pitch variation axis I-I (FIG. l), and which hold, at their peripheries, the bundles 5, 6, 7, 8.

These holding means comprise in addition sheets 9 and 10 which connect respectively, at the interior of the volume of the arm and along at least a part of their length, the opposite bundles 5, 7, and 6, 8, and these sheets 9 and 10 pass through the pitch variation axis I-I.

The sheet 9, also called drag web for reasons which will be seen hereafter, advantageously has the same prole as the arm 3, such as this arm appears in FIG. 1, and this sheet 9 is inserted between two consecutive median strips of the bundles of strips 5 and 7. The sheet 9 is advantageously provided, adjacent to the hub body 2, with a rst indentation 13, and adjacent to the blade 4, with a second indentation 14.

ICC

The sheet 10, also called flapping web, advantageously has the same profile as the arm 3, such as this arm appears in FIG. 2, and this sheet is inserted between two consecutive median strips of the bundles of. strips 6 and 8. The sheet 10 is also provided, adjacent to the hub body 2, with an indentation 15, and adjacent to the blade 4, with an indentation 16.

In the example described, the sheets 9 and 10 intersect each other at right angles at the interior of the arm along the axis I-I. Although other embodiments are possible, it is advantageous to form the sheet 10 for example in two parts ('FIG. 3) disposed on opposite sides of the sheet 9 and joined to this sheet 9 by rivets 17 or any other mode of connection.

The braces 11 (of which a group of four, assembled in a collar, is represented in FIG. 3) are advantageously constituted by channel bars of U cross-section, provided at their ends with recesses 18 permitting them to bear against two consecutive bundles of strips such as 5 and 6. The bottom of the U, the bundles 5 to 8 and the sheets 9 and 10, although in section in FIG. 3, are not shown there with cross-hatching, in order to render the drawing more clear. Once mounted, each brace bears, on the one hand, by the recesses 18 of its ends, against half of the strips of the corresponding 'bundles of strips, and on the other hand, by flats 19 provided on the bottom of its channel bar, against the sheets 9 and 10. The braces 11 are placed, as shown in FIGS. 1 and 2, such that their ats 19 are disposed facing each other in pairs, on opposite sides of the sheets 9 and 10. The braces 11 are disposed by groups of four regularly spaced along the arm 3. The four braces 11 of each group are fixed to each other by rivets 20 (FIG. 3), or any other mode of connection, which press the ats 19 of neighbouring braces against the sheets 9 or 10 separating them. The braces 11, once fixed to each other in a group of four, clamp the bundles of strips engaged in the adjacent recesses 18 and the sheets 9 and 10. The ensemble of the braces 11 and the sheets 9 and 10 thus assures the holding of the bundles of strips and confers on the arms 3 appropriate resistances to exion and to torsion, as will be explained during the description of the operation of the hub as a whole.

Advantageously forks 12 are provided, which are disposed on each bundle between the groups of braces 11, and which clamp the strips of the bundle.

These forks 12 are advantageously constituted by two channel bars of U cross-section, each channel bar bearing against half of the strips of a bundle of strips and against the corresponding sheet 9 or 10, by a recess and a at (not visible in the figures) in a manner analogous to the manner which has been described for the ends of the braces 11. The two channel bars of each fork 12 are disposed back to back on a bundle, and when these two channel bars are fixed by rivets 21, or any other mode of connection, these channel bars press the strips of the bundle in question and hold it with respect to the corresponding sheet 9 or 10. These forks 12 are disposed at regular intervals on the four bundles 5, 6, 7 and 8 between the groups of braces 11.

In the example described the hub body 2 is advantageously constituted by a pile of sheets which can be glued to each other, and this hub body has approximatively the form of a star having three branches 22 between which are provided three indentations 23.

Each arm 3, fixed to a branch 22 of the hub body 2 by fastening means described hereafter, is disposed, with respect to the hub body 2, in the particular case represented, such that the bundles 5 and 7 which separate the most from each other are at least approximatively in the plane of the hub body, and such that the bundles 6 and 8 which separate from each other the least are in a perpendicular plane passing at least approximatively through the axle 1 of the rotor.

These fastening means are advantageously constituted by fork-joints 24, 25, 26 and 27 connected respectively to the neighbouring ends of the bundles 5, 6, 7 and 8.

The fork-joints 24 and 26 are bolted to the hub body 2, on the sides of each branch 22, symmetrically about the pitch variation axis I--I (FIG. l) which coincides with the axis of symmetry of that branch 22. These forkjoints 24 and 26 respectively hold the ends of the bundles of strips 5 and 7 by means of bolts 30 and 31.

Supports 28 and 29 are disposed on both faces of the branch 22 being considered, at its free end, such that the fork-joints 25 and 27 which they carry or of which they form part are disposed on opposite sides of the plane of the hub body 2.

This free end of the branch 22 penetrates into the interior of the arm 3 in the space left by the indentations 13 and 15 of the sheets 9 and 10, and this free end comprises an indentation 32 whose contour is symmetrical about the axis I-I.

Each support 28 or 29 bears against the branch 22 of the hub body 2 by a rounded projection 33 (FIG. 4), 'which is located between the axle 1 and the bottom of the indentation 32, and by heels 34 located on opposite sides of this indentation. The supports 28 and 29 are fixed to the branch 22 by bolts 35 and 36 which pass through both of the supports, the branch 22 and two of the heels 34. These two heels thus press between themselves the pile of thin sheets of the branch 22 on both sides of the indentation 32. In addition, a bolt 37, passing through the supports 28, 29 and the branch 22 between the projections 33 and the bottom of the indentation 32, clamps these projections 33 against the pile of sheets of the branch 22. The hole 38 permitting the passage of the bolt 37 in the branch 22 is of a diameter greater than the diameter of the shaft 39 of the bolt 37 in order that this shaft 39 does not come into contact with the sheets of the branch 22 when the free end of that branch bends under the action of the supports 28 and 29, which is the case as will be seen hereafter.

The fork-joints 25 and 27 respectively hold the ends of the bundles 6 and 8, in a plane containing the axis I-I and perpendicular to the plane of the hub body 2, by means of bolts 40 and 41.

Each arm 3 is provided, at its end situated adjacent to the blade, with a fitting 42 comprising four fork-joints 43, 44, 45 and 46 to which are respectively fixed, by bolts 54, the ends of the bundles 5, 6, 7 and 8. The fitting 42 also carries mechanical means, represented in FIGS. l and 2, adapted to hold the blade 4. This blade, rigidly secured to the attachment plate l48, is articulated about a spindle A47. Mechanical means, for example an hourglass screw, can be provided to permit the blade to be folded, by pivoting about the spindle 47, into parking position.

Each arm 3 is provided with a control arm 49 (FIG. 5) fixed to the fitting 42 and rigid in flexion and in torsion. In the example indicated, it is disposed approximatively in the plane of the hub body 2 and is connected by its free end 50 to a pitch control means such as 51, 52, S3 of a type known in itself.

Needless to say, the arms 3, the control arms 49 and the pitch control device can be contained in stream-lining (not shown) conferring on them good faculties of penetration in the air.

The operation of the rigid hub described above will now be described.

Each arm 3 connected to a blade 4 is subjected, independently of the centrifugal force due to the overall rotation of the blades, to various forces due to the three movements that the blade can perform.

When one of the blades 4 performs a drag movement, the bundles of strips 5 and 7 are alternately subjected to traction and compression forces. If it is assumed that the bundle of strips 5 is urged in traction and the bundle of strips 7 is urged in compression, the arm 3 offers a high resistance to such urging, due to the traction exerted on the bundle and to the rigidity to an edge-wise force presented by the sheet 9 holding the bundles 5 and 7 substantially in position with respect to each other. The bundle 5 is stretched and rectilinear and it thus ensures, due to the various groups of four braces 11, the holding of the ensemble of the four bundles 5, `6, 7 and 8 and, in particular, of the bundle 7 which, urged in compression, has a tendency towards buckling. The forks 12 serve to hinder local buckling of the strips of the bundle 7, between the groups of braces 11, when this bundle 7 is urged in compression. Without these collars, the strips of the bundle 7 could have a tendency to separate from Veach other. The phenomena are analogous for the other possible case in which the bundle 5 is urged in compression and the bundle 7 in traction.

It should be noted that, for the drag movements of each blade 4, the hub body 2 and its branches 22 possess a high rigidity in the direction of this movement and that the ensemble of the hub body and of the connecting arms thus offers a high resistance to the drag movements.

When the blade 4 performs a flapping movement, the bundles of strips y6 and y8 are in their turn subjected alternately to forces of traction and of compression, and the sheet 10, which acts as a web for the bundles `6 and 8, is subjected to edgewise forces. For the same reasons as above, the arm 3 offers a high resistance to such urging. Nevertheless, the forces of traction and of compression applied to the bundles 6 and 8 are transmitted to the fork-joints 25 and 27, themselves rigidly secured to the supports 28 and 29. These forces create a moment applied to the two supports 28 and 29 about their projections 33. This moment bends the branch 22 as a whole, and by the intermediary of the supports 28 and 29, the part of the branch 22 which is clamped between these supports. This latter bending or flexion is facilitated by the presence of the indentation 32 and by the fact that the moment is applied to the branch 22 by the heels 34 which are situated at the end of that branch. The ensemble of the hub body 2 with its branch 22 and of the connecting arm 3 thus presents a relative flexibility for the flapping movements of the blade 4, in spite of the high resistance of the arm 3 to such a movement. It should be noted that the centrifugal force created by the movement of the blade is absorbed in shear by the shafts of the bolts 35 and 36, since the shaft 39 of the bolt 37 is not in contact with the branch 22, even for the exions described above. Moreover, the flexibility of the ensemble of the branch 22 and of the arm 3 for the flapping movements can be regulated by modifying the length of the supports 2'8 and 29.

Finally, the resistance to torsion of each arm 3 according to the invention is relatively low. This permits the pitch variation of each blade to be controlled by applying to the end of each arm 3, adjacent to the blade, an appropriate torsion couple. This is achieved due to the pitch control system which applies, to the end 50 of the control arms `49, forces directed parallel to th e axle 1 of the rotor.

The flapping movements and the drag movements of the blade 4 result from an equilibrium between the forces acting on these blades and the mechanical reactions of the arms 33 according to the invention, and the pitch variation of the blades is controlled by the pitch control device.

The rigid hub, constructed vwith arms according to the invention, presents numerous advantages among which can be cited:

good manoeuvreability;

for a rotor craft, very good damping of the rolling and pitching movements of the craft;

simplicity of construction;

reduction of maintenance costs;

lightness.

What I claim is:

1. Hub and rotor blade system having variable pitch blades, which comprises a rotary axle, a hub body rigidly secured to this axle, arms fixed in non-articulated manner to said hub body and said rotor blades xed at the free ends of said arms, each arm comprising at least three bundles of piled strips which bundles are distributed about the pitch variation axis of the blade xed to said arm, the bundles of strips of any one arm being connected to each other and to the hub body by holding means such that the strips are not bonded together whereby the arm possesses a high resistance to llexion and a relatively low resistance to torsion.

2. Hub according to claim 1, wherein the holding means comprise rigid collars which are disposed at a distance from each other in planes approximately perpendicular to the pitch variation axis, each of these collars maintaining, at its periphery, the bundles.

3. Hub according to claim 1, wherein the holding means comprise sheets which pass through the pitch variation axis and which connect the bundles together along at least a part of their length.

4. Hub according to claim 2, wherein each collar is formed of braces, constituted by channel bars of U crosssection, which are joined together, back-to-back, by their ends and which comprise, at these ends, recesses in which the bundles of strips are engaged and clamped.

5. Hub according to claim 1:

wherein the holding means comprise rigid collars which are disposed at a distance from each other in planes approximatively perpendicular to the pitch variation axis, each of these collars maintaining, at its periphery, the bundles;

wherein the holding means further comprise sheets which pass through the pitch variation axis and which connect the bundles together along at least a part of their length;

wherein each collar is formed of braces, constituted by channel bars of U cross-section, which are joined together, back-to-back, by their ends and which comprise, at these ends, recesses in which the bundles of strips are engaged and clamped;

and wherein the braces comprise, at their ends, flats bearing against the sheets by which they are xed to said sheets.

6. Hub according to claim 5, wherein said ilats of two adjacent brace ends bear against the corresponding sheet on opposite sides of this sheet, and a fastening member holds the pile constituted by the two flats and the sheet inserted between them.

7. Hub according to claim 6, wherein the fastening nlilember is a rivet passing through the two llats and the s eet.

'8. Hub according to claim 2, wherein forks are inserted between the collars along each bundle of strips, these forks clamping the strips of the bundle.

9. Hub according to claim -8, wherein each fork is constituted by two channel bars of U cross-section which are joined together, back-to-back, by two of their ends and which comprise, at the other ends, recesses in which a bundle of strips is housed and clamped.

10. Hub according to claim 9:

wherein the holding means comprise sheets which pass through the pitch variation axis and which connect the bundles together along at least a part of their length;

wherein the ends by which the two channel bars of a fork clamping a bundle of strips are joined together comprise flats which bear against the sheet, connected to this bundle, on opposite sides of this sheet;

and wherein the ensemble of the two channel bars of each fork and the corresponding sheet is held by a rivet passing through the two ilats and the sheet.

11. Hub according to claim 1, wherein the hub body has approximately the form of a star having as many branches as there are blades.

12. Hub according to claim 11, wherein at least certain of the bundles of each arm are not disposed in the plane of the hub body, and wherein these certain bundles are connected to the corresponding branch of the star by the intermediary of fork-joints xed to said branch by supports.

13. Hub according to claim 12, wherein each support bears against a branch by at least two bearing members one of which is a heel having a plane bearing face and the other of which is a rounded projection, the heal being placed near to the end of the branch and the projection being placed near to the rotary axle at a distance from the heel which determines the resistance to ilexion of the ensemble of the branch and the arm in a plane containing the rotary axle and the pitch variation axis.

14. Hub according to claim 13, wherein each support is fixed to a branch by at least one bolt passing through the support, the heel and the branch and at least one bolt passing through the support near to the projection and the branch, this latter bolt applying with force the projection against the hub body.

15. Hub according to claim 11, wherein certain of the bundles of each arm are disposed in the plane of the hub body, and wherein these certain bundles are connected to a branch by the intermediary of fork-joints fixed directly to the sides of the branch.

16. Hub according to claim 11, wherein the sheets comprise, adjacent to the hub body, indentations permitting the end of the branch to penetrate at least partially into the interior of the arm.

17. Hub according to claim 1, wherein each arm is provided, at its end remote from the hub body, with a blade attachment tting comprising fork-joints to which the bundles are respectively fixed.

18. Hub according to claim 1, wherein each arm comprises four bundles of strips disposed along the edges of a pyramid having a diamond-shaped base and whose summit is remote from the hub body and whose height is substantially coincident with the pitch variation axis, the bundles being disposed substantially in the planes joining the opposite edges of said pyramid, the two bundles which separate the farthest from the pitch variation axis being approximately in the plane of the hub body and the two other bundles being in the plane passing through the rotary axle and through the pitch variation axis.

19. Hub according to claim 18, wherein the edges of the sheets are inserted in the bundles of piled strips, between two neighboring strips of the median part of the piles constituting the bundles.

20. Hub according to claim 18, wherein the sheet which connects the two bundles which separate the farthest from the pitch variation axis forms a single piece disposed in the plane passing through the edges of the pyramid which correspond to these two bundles, and the sheet which connects the other two bundles is formed of two pieces disposed on opposite sides of the single-piece sheet, in the plane passing through the edges of the pyramid which correspond to these other two bundles, the two pieces of the two-piece sheet being lixed rigidly to the single-piece sheet in the neighborhood of the pitch variation axis.

21. Hub according to claim 18, wherein supports are provided, which hold the said other two bundles and which are disposed facing each other on opposite sides of the branch, said supports comprising two heels disposed symmetrically about the plane passing through the pitch variation axis and through the rotary axle, and wherein the branch comprises an indentation whose contour is symmetrical about said plane and which extends between the heels and as far as the vicinity of the projection.

22. Hub according to claim 17, wherein each arm is provided with a pitch control arm which is fixed to the blade attachment fitting and which extends from this tting towards the hub body in a direction moving away from the pitch variation axis.

References Cited UNITED STATES PATENTS 2,949,967 `8/ 1960 Jovanovich 416-134 3,310,119 3/1967 Watson 416-159 3,384,185 5/ 1968 Fernandez 416-244 3,261,407 7/1966 Culver et al. 416-138,(UX) 3,330,362 7/1967 Kastan 416-132(X) FOREIGN PATENTS 692,503 8/1930 France 416-168 1,334,446 7/1963 France 416-134 1,442,684 5/1966 France 416-140 EVERETTE A, POWELL, JR., Primary Examiner 

